Annual report pursuant to Section 13 and 15(d)

Securities - Additional Information (Detail)

v3.6.0.2
Securities - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]      
Debt and equity securities OTTI charge $ 0    
Impairment charges on securities in continuous unrealized loss position for 12 months or longer 0 $ 0  
Net realized gain (loss) on redemption or sale of investment securities 46,000 6,611,000 $ 2,011,000
Net unrealized gains (losses) recognized in earnings resulting from the redemption of investment securities (314,000) (1,900,000) $ (498,000)
Investment securities available-for-sale, market values 516,964,000 698,296,000  
Securities Pledged as Collateral [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Investment securities available-for-sale, market values 133,000,000 72,000,000  
Mortgage-backed securities [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Estimated fair value of collateral 52,900,000 58,600,000  
Investment securities available-for-sale, market values $ 229,630,000 $ 284,381,000